Use of saccharin for stabilizing thermoplastic, aromatic polycarbonates

ABSTRACT

A thermoplastic molding composition comprising aromatic polycarbonate, saccharine and a compound having at least one ester group in its structure is disclosed. The inventive composition is characterized in its improved stability and hence suitable for the preparation of stable films, compact discs and sheets.

Thermoplastic aromatic polycarbonates are in themselves thermallystable. If these polycarbonates contain low molecular weight additivescontaining ester groups, for example mould release agents, a slightreduction in the molecular weight of the aromatic polycarbonates occursin the melt, for example during extrusion or during injection mouldingtreatment, as a result of transesterification with the additive. Thisdisadvantage is of consequence in the event of repeated processing ofthese additive-containing polycarbonates or indeed in the event ofre-use of polycarbonate waste material.

This disadvantage arises in particular when the thermoplasticpolycarbonate contains impurities in the form of traces of alkalicompounds, alkaline-earth compounds or heavy metal compounds.

It has surprisingly been discovered that the addition of saccharine inamounts of from 0.001 wt. % to 5.0 wt. %, preferably from 0.005 wt. % to1.5 wt. %, extensively prevents this undesirable transesterification ofaromatic polycarbonates which contain additives containing ester groups.

The present invention thus provides the use of saccharine in amounts offrom 0.001 wt. % to 5.0 wt. %, preferably from 0.005 wt. % to 1.5 wt. %,based on 100 wt. % polycarbonate, to stabilise thermoplastic aromaticpolycarbonates which contain from 0.01 wt. % to 5 wt. %, preferably from0.05 wt. % to 3 wt. %, again based on 100 wt. % polycarbonate, of estergroup-containing additives.

The present invention further provides polycarbonate mouldingcompositions containing

A) 100 wt. % thermoplastic aromatic polycarbonate, and additionally

B) 0.001 wt. % to 5.0 wt. %, preferably from 0.005 wt. % to 1.5 wt. %,based on 100 wt. % of A, of saccharine, and additionally

C) 0.01 wt. % to 5 wt. %, preferably from 0.05 wt. % to 3 wt. %, againbased on 100 wt. % of A, of ester group-containing additives.

Thermoplastic aromatic polycarbonates covered by the present inventioninclude both homopolycarbonates and copolycarbonates; the polycarbonatesmay, in known manner, be either linear or branched.

These polycarbonates are produced in the known way from diphenols,carbonic acid derivatives, optionally chain terminators and optionallybranching agents.

Details of polycarbonate production are to be found in many patentspecifications filed over approximately the last 40 years. Referencewill be made here, by way of example, merely to Schnell, “Chemistry andPhysics of Polycarbonates”, Polymer Reviews, Volume 9, IntersciencePublishers, New York, London, Sydney 1964, to D. Freitag, U. Grigo, P.R. Müller, H. Nouvertne', BAYER AG, “Polycarbonates” in Encyclopedia ofPolymer Science and Engineering, Volume 11, Second Edition, 1988, pages648-718 and finally to Drs. U. Grigo, K. Kircher and P. R. Müller“Polycarbonates” in Becker/Braun, Kunststoff-Handbuch, Volume 3/1,Polycarbonates, Polyacetals, Polyesters, Cellulose Esters, Carl HanserVerlag Munich, Vienna 1992, pages 117-299.

Diphenols suitable for producing polycarbonates are, for example,hydroquinone, resorcinol, dihydroxydiphenyls, bis(hydroxyphenyl)alkanes,bis(hydroxyphenyl)cycloalkanes, bis(hydroxyphenyl) sulfides,bis(hydroxyphenyl) ethers, bis(hydroxyphenyl) ketones,bis(hydroxyphenyl) sulfones, bis(hydroxyphenyl) sulfoxides,α,α′-bis(hydroxyphenyl)-diisopropylbenzenes, together with theirring-alkylated and ring-halogenated compounds.

Preferred diphenols are 4,4′-dihydroxydiphenyl,2,2-bis-(4-hydroxyphenyl)propane,2,4-bis-(4-hydroxyphenyl)-2-methylbutane,1,1-bis-(4-hydroxyphenyl)-p-diisopropyl-benzene,2,2-bis-(3-methyl-4-hydroxyphenyl)propane,2,2-bis-(3-chloro-4-hydroxyphenyl)propane,bis-(3,5-dimethyl-4-hydroxyphenyl)methane,2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)propane,bis-(3,5-dimethyl-4-hydroxyphenyl) sulfone,2,4-bis-(3,5-dimethyl-4-hydroxyphenyl)-2-methylbutane,1,1-bis-(3,5-dimethyl-4-hydroxyphenyl)-p/m-diisopropylbenzene,2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane,2,2-bis-(3,5-dibromo-4-hydroxyphenyl)propane,1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane,1,1-bis-(4-hydroxyphenyl)-1-phenylethane and1,1-bis-(4-hydroxyphenyl)cyclohexane.

Diphenols which are particularly preferred are2,2-bis-(4-hydroxyphenyl)propane,2,2-bis-(3,5-dimethyl-4-hydroxy-phenyl)propane,2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane,2,2-bis-(3,5-dibromo-4-hydroxyphenyl)propane,1,1-bis-(4-hydroxyphenyl)cyclohexane and1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane.

These and other suitable diphenols are described, for example, in U.S.Pat. Nos. 3,028,635, 2,999,835, 3,148,172, 2,991,273, 3,271,367,4,982,014 and 2,999,846, in German published patent applications 1 570703, 2 063 050, 2 036 052, 2 211 956 and 3 832 396, French patentspecification 1 561 518, the monograph “H. Schnell, Chemistry andPhysics of Polycarbonates, Interscience Publishers, New York 1964” andin Japanese published patent applications 62039/1986, 62040/1986 and105550/1986.

In the case of homopolycarbonates, only one diphenol is used, whereas,in the case of co-polycarbonates, several diphenols are used.

Suitable carbonic acid derivatives are, for example, phosgene ordiphenyl carbonate.

Both monophenols and monocarboxylic acids are suitable for use as chainterminators. Suitable monophenols are phenol itself, alkylphenols suchas cresols, p-tert.-butylphenol, p-n-octylphenol, p-iso-octylphenol,p-n-nonylphenol, and p-iso-nonylphenol, halophenols such asp-chlorophenol, 2,4-dichlorophenol, p-bromophenol and2,4,6-tribromophenol together with mixtures thereof.

Suitable monocarboxylic acids are benzoic acid, alkyl-benzoic acids andhalobenzoic acids.

Preferred chain terminators are phenols of the formula (I)

in which

R is a branched or unbranched C₈ and/or C₉ alkyl residue.

The quantity of chain terminator to be used amounts to from 0.1 mol % to5 mol %, based on the number of mol of the diphenols used in each case.Chain terminators may be added before, during or after phosgenation.

Suitable branching agents are the trifunctional or more thantrifunctional compounds known in polycarbonate chemistry, in particularthose with three or more than three phenolic OH groups.

Suitable branching agents are, for example, phloroglucinol,4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)-2-heptene,4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)heptane,1,3,5-tri-(4-hydroxyphenyl)benzene, 1,1,1-tri-(4-hydroxyphenyl)ethane,tri-(4-hydroxyphenyl)phenylmethane,2,2-bis-[4,4-bis-(4-hydroxyphenyl)cyclohexyl]propane,2,4-bis-(4-hydroxyphenyl-isopropyl)phenol,2,6-bis-(2-hydroxy-5′-methylbenzyl)-4-methylphenol,2-(4-hydroxyphenyl)-2-(2,4-dihydroxyphenyl)-propane,hexa-(4-(4-hydroxyphenylisopropyl)phenyl)-orthoterephthalic acid ester,tetra-(4-hydroxyphenyl)-methane,tetra-(4-(4-hydroxyphenylisopropyl)phenoxy)-methane and1,4-bis-(4′,4″-dihydroxytriphenyl)methyl)-benzene together with2,4-dihydroxybenzoic acid, trimesic acid, cyanuric chloride and3,3-bis-(3-methyl-4-hydroxyphenyl)-2-oxo-2,3-dihydroindole.

The quantity of branching agent optionally to be used amounts to from0.05 mol % to 2 mol %, again based on the number of mol of the diphenolsused in each case.

The branching agents may either be present with the diphenols and thechain terminators in the initial aqueous alkaline phase or be added insolution in an organic solvent prior to phosgenation. In the case of atrans-esterification process, the branching agents are added togetherwith the diphenols.

All these measures for producing thermoplastic polycarbonates arefamiliar to the person skilled in the art.

The polycarbonates to be used according to the invention have averageweight average molecular weights Mw, determined by measuring therelative viscosity in CH₂Cl₂ at 25° C. with a concentration of 0.5 g in100 ml CH₂Cl₂, of between 10,000 and 80,000, preferably between 15,000and 40,000.

Ester group-containing additives for thermoplastic polycarbonates are,in particular, plasticisers and mould release agents, as described inthe literature and also used for processing thermoplasticpolycarbonates.

The ester group-containing additives according to component C) may becompletely esterified compounds or partial esters with non-esterified OHgroups or non-esterified carboxyl groups.

The ester group-containing additives according to component C) aresynthesised from aliphatic monoalcohols, aliphatic dialcohols, aliphatictrialcohols, aliphatic tetrols, aliphatic pentols and/or aliphatichexols having 1 to 15 C atoms, preferably 2 to 10 C atoms andparticularly preferably 3 to 6 C atoms, and aliphatic monocarboxylicacids, aliphatic dicarboxylic acids and/or aliphatic tricarboxylic acidshaving 3 to 34 C atoms, preferably 10 to 24 C atoms and particularlypreferably 12 to 18 C atoms.

The ester group-containing additives have average molecular weights n(number average, determined by end group assay) of from 100 to 3000,preferably from 300 to 1000.

Examples of aliphatic alcohols are ethanol, propanol, butanol, ethyleneglycol, glycerol, pentaerythritol, 1,4-butanediol, 1,6-hexanediol,1,10-decanediol, hexanol, n-decyl alcohol, lauryl alcohol, myristylglycol, t-amyl alcohol, 1,2,4-butanetriol, 1,2,6-hexanetriol, inositol,sorbitol, erythritol and xylitol.

Examples of aliphatic carboxylic acids are butyric acid, isovaleric,caproic, caprylic, capric, lauric, myristic, palmitic, stearic,arachidic, behenic, lignoceric and cerotic acid, malonic acid, succinicacid, glutaric acid, adipic acid, sebacic acid, dodecanedioic acid andthapsic acid.

Examples of ester group-containing additives according to component C)are ethyl stearate, glycerol monostearate, distearate and tristearate,butyl laurate, hexyl laurate, pentaerythritol tetralaurate,tetrapalmitate, tetra-stearate, pentaerythritol trilaurate, tripalmitateand tristearate, sebacic acid monobutyl ester and dibutyl ester togetherwith dodecanedioic acid monobutyl ester and dibutyl ester.

The ester group-containing additives are known from the literature ormay be produced according to processes known from the literature. (Seefor example U.S. Pat. No. 3,186,961, JA-Sho-47-41092, U.S. Pat. No.3,784,595, JA-Sho-49-11949, JA-Sho-49-55752 and U.S. Pat. No.4,131,575.)

The saccharine used according to component B) in the mouldingcompositions according to the invention is normal saccharine asavailable internationally in pharmaceutical grade under the names“Saccharine 550” or “insoluble saccharine”.

It exhibits the formula

It should preferably be free of alkali ions, in particular sodium ions,or may contain at most 100 ppm alkali ions, in particular sodium ions.

Contaminated saccharine arising during production has therefore to bepurified prior to use according to the invention in the known way byrecrystallisation.

A controlled release powder is known from DE-OS 3 538 429 for use inedible pharmaceutical and other compositions, said powder beingcharacterized in that it contains individual micro-particles whichcontain an active component and optionally an excipient mixed intimatelywith at least one non-toxic polymer (claim 1).

Polycarbonate is mentioned, inter alia, as the polymer (claim 5), whilesaccharine is named as the active component. (Page 13, lines 36/37 ofthe DE-OS). Surface active agents may act as the excipient (page 18,lines 13 to 33 of the DE-OS) (of also the corresponding U.S. Pat. No.5,354,556).

Use according to the invention is not affected thereby, since theinvention does not seek to achieve controlled release.

Cell and tissue culture substrates are known from DE-OS 3 743 136, whichconsist of synthetic materials and may contain one or more specialcompounds. Polycarbonate may also serve as the synthetic material (claim1 of DE-OS 3743136), saccharine acting as the special compound (claim24).

Use according to the invention is not affected thereby. According toU.S. Pat. No. 4 782 103, polycarbonates containing UV stabilisers areknown which additionally contain sulfonimides. Saccharine may also beused for this purpose. (Column 2, line 16). Mould release agents mayalso be added (column 3, line 20). However the object of the U.S. patentis different.

In EP-A 0 742 260 (Le A 30 889-EP), saccharine is used to stabilisethermoplastic polycarbonates against the discolouring effect of β,γrays. (Page 1 of the application).

Other mould release agents may also be added (page 5, line 13), butester group-containing additives are not mentioned.

The object of EP-A 0 742 260 does not permit any conclusions to be drawnas to the synergistic effect according to the present invention.

Components B) and C) may be worked into the thermoplastic polycarbonateresins in the known way either by means of the melt at temperatures offrom 200° C. to 360° C., preferably from 260° C. to 320° C., or bydissolving the polycarbonates in known inert solvents such as CH₂Cl₂.

The melt, including the components B) and C) mixed therein, is extractedvia the extruder, cooled and pelletised.

The polycarbonate solutions, including the components B) and C), areconcentrated and either formed directly into films by pouring orevaporated via the extruder and pelletised or precipitated out of thesolutions by the addition of known precipitating agents such as tolueneand isolated as a powder.

The polycarbonate moulding compositions according to the invention maybe processed in the known way to form any desired moulded articles, forexample they may be injection moulded using known machines attemperatures of from 200° C. to 360° C. Examples of such mouldedarticles other than films, are solid sheets, twin-walled sheets andcompact discs.

The present invention thus also provides use of the polycarbonatemoulding compositions according to the invention for the production offilms, solid sheets, twin-walled sheets and compact discs.

Other conventional additives, such as for example organic phosphites,optionally combined with monomeric or oligomeric epoxides, flameretardants, in particular those containing fluorine, such aspolyperfluoroethylene, colouring agents, pigments, anti-static agents,fillers and reinforcing materials, may also be added in conventionalamounts to the polycarbonate moulding compositions according to theinvention before, during or after processing thereof.

Other thermoplastics may also be added, for generally non-transparentapplications, in the known way to the polycarbonate mouldingcompositions according to the invention in amounts of from 2 wt. % to 30wt. %, preferably from 5 wt. % to 25 wt. % and in particular from 8 wt.% to 20 wt. %, based on 100 wt. % polycarbonate resin.

Other suitable thermoplastics are, for example, aromatic polyestercarbonates, polyalkylene terephthalate, EPDM polymers, polystyrene andstyrene-based co- and graft copolymers, such as in particular ABS.

The polycarbonate moulding compositions according to the invention maybe used as moulded articles wherever thermoplastic polycarbonates havehitherto been used, that is to say in vehicle construction, theelectrical industry, as safety partitions, roof coverings in thebuilding industry, as lamp covers, prisms and in data storagetechnology.

EXAMPLES

The following data were measured using test plates.

The following test plates were obtained by compounding of theabove-mentioned compositions using a twin screw extruder ZSK 32 andsubsequent production of the test plates by the injection mouldingprocess.

Compounding: composition temperature 300° C. Test piece production:composition temperature 300° C.; mould temperature 90° C.

Test 1 Solution viscosity Composition (η_(rel)) MVR Reextrudedpolycarbonate 1.282  8.42 Polycarbonate + 0.75% PPG 1.286  9.16Polycarbonate + 0.75% PPG + 0.5% Saccharine A 1.278 11.26Polycarbonate + 0.75% PPG + 0.5% Saccharine B 1.279 12.12

Saccharine A: Na content according to atomic absorption: 24 ppm/27 ppm

Saccharine B: Na content according to atomic absorption: 2500 ppm/2500ppm

Polycarbonate: Macrolon 2808 made by Bayer AG was used, having asolution viscosity of (η_(rel))=1.294

MVR: according to ISO 1133A, at 300° C. and a weight of 1.2 kg

%: percentage by weight in the total mixture

PGG: polypropylene glycol having an average molecular weight (weightaverage) of approximately 2500.

As the values show, the solution viscosities and the melt viscosities ofthe two saccharine-containing compounds differ only insignificantlywithin the margins of error, although the Na content varies markedly.

Replication of the test produced the following results:

Test 2 Solution viscosity Composition (η_(rel)) MVR Reextrudedpolycarbonate 1.288  7.82 Polycarbonate + 0.75% PPG 1.287  9.03Polycarbonate + 0.75% PPG + 0.5% Saccharine A 1.279 10.29Polycarbonate + 0.75% PPG + 0.5% Saccharine B 1.278 10.50

The results of the first test are confirmed: no significant reduction insolution viscosity and no increase in MVR.

Two sterilisation cycles subsequently carried out at 125° C. under steamusing the test plates obtained in the above test produced the followingvalues:

Solution viscosity (η_(rel)) 1st 2nd Composition Start cycle cycleReextruded polycarbonate 1.288 1.289 1.288 Polycarbonate + 0.75% PPG1.287 1.286 1.285 Polycarbonate + 0.75% PPG + 0.5% Saccharine A 1.2791.278 1.279 Polycarbonate + 0.75% PPG + 0.5% Saccharine B 1.278 1.2801.278

Again, there is no notable variation in the values. Thus, nosuperproportional hydrolysis has occurred, as would have been expectedin the compounds containing saccharine B owing to its high sodiumcontent.

What is claimed is:
 1. A polycarbonate molding composition comprising:A) 100 wt. % thermoplastic aromatic polycarbonate; B) 0.001 wt. % to 5.0wt. %, based on 100 wt. % of A), of insoluble saccharin containing lessthan 100 ppm alkali ions; and C) 0.01 wt. % to 5 wt. %, based on 100 wt.% of A), of an ester group-containing additive.
 2. The polycarbonatemolding composition of claim 1 wherein said insoluble saccharin B) isfree of alkali ions.
 3. Films, prepared from the polycarbonate moldingcomposition of claim
 1. 4. Cladding sheets, prepared from thepolycarbonate molding composition of claim
 1. 5. Polymer twin-walledsheets, prepared from the polycarbonate molding composition of claim 1.6. Compact discs, prepared from the polycarbonate molding composition ofclaim
 1. 7. A thermoplastic molding composition comprising: (A) aromaticpolycarbonate; (B) 0.001 to 5.0 percent of insoluble saccharincontaining less than 100 ppm alkali ions; and (C) 0.01 to 5 percent of acompound having a number average molecular weight of 100 to 3000, saidcompound having at least one ester group in its structure, said percentsbeing relative to the weight of said composition.
 8. The composition ofclaim 7 wherein said compound (C) is a plasticizer.
 9. The compositionof claim 7 wherein said compound (C) is a mold release agent.
 10. Thecomposition of claim 7 wherein said compound (C) is completelyesterified.
 11. The composition of claim 7 wherein said compound (C) isa partial ester containing non-esterified OH groups.
 12. The compositionof claim 7 wherein said compound (C) is a partial ester containing atleast one non-esterified carboxyl group.
 13. The composition of claim 7wherein said compound (C) is a product of a reaction of: (i) at leastone member selected from the group consisting of C₁₋₅ aliphaticmonoalcohol, aliphatic dialcohol, aliphatic trialcohol, aliphatictetrol, aliphatic pentol and aliphatic hexol; with (ii) at least onemember selected from the group consisting of C₃₋₃₄ aliphaticmonocarboxylic acid, aliphatic dicarboxylic acid and aliphatictricarboxylic acid.
 14. An article of manufacture comprising thecomposition of claim
 7. 15. The thermoplastic molding composition ofclaim 7 wherein said insoluble saccharin (B) is free of alkali ions.